关闭可能引发异常的资源

Question

• Connection从池中获取(这可能会引发异常)
• 创建一个Statement连接(也可能抛出异常)
• 使用该语句执行SQL查询并将其存储在ResultSet(也可以抛出)中
• 用查询结果做一些事情
• 关闭ResultSet(例外!)
• 关闭Statement(例外!)
• 关闭Connection(例外!)

---

看看这段代码:

    Connection  conn = null;
    Statement   st   = null;
    ResultSet   set  = null;
    try {
        conn    = Database.getConnection();
        st      = conn.createStatement();
        set     = st.executeQuery("SELECT * FROM THING");

        // <-- Do stuff
    } catch (Exception e) {

    } finally {
        // Close set if possible
        if (set != null) {
            try {
                set.close();
            } catch (Exception e) {

            }
        }

        // Close statement if possible
        if (st != null) {
            try {
                st.close();
            } catch (Exception e) {

            }
        }

        // Close connection if possible
        if (conn != null) {
            try {
                conn.close();
            } catch (Exception e) {

            }
        }
    }

---

该finally区块是我收我的东西.如你所见,它非常混乱.我的问题是:这是清理这些资源的正确方法吗？

Answer 1

在Java 1.7之前,您的代码是捕获可关闭资源的异常的正确方法,除了您应该捕获SQLException而不是Exception.

从Java 1.7开始,您可以使用"try-with-resources"语句,该语句允许您声明close()在try块完成时自动调用的资源,从而节省样板finally代码.

try (Connection conn = Database.getConnection(); Statement st = conn.createStatement();
     ResultSet set = st.executeQuery("SELECT * FROM THING")) {
   // Your "try" code as before
}
catch (SQLException e) {
   // Handle as before
}
// No "finally" to clean up resources needed!